title: Inhibition of late-stage autophagy synergistically enhances pyrrolo-1,5-benzoxazepine-6-induced apoptotic cell death in human colon cancer cells.
abstract: The pyrrolo-1,5-benzoxazepines (PBOXs) are a novel group of selective apoptotic agents displaying promising therapeutic potential in both ex vivo chemotherapy-refractory patient samples and in vivo murine carcinoma models. In this report, we present novel data concerning the induction of autophagy by the PBOXs in adenocarcinoma-derived colon cancer cells. Autophagy is a lysosome-dependent degradative pathway recently associated with chemotherapy. However, whether autophagy facilitates cell survival in response to chemotherapy or contributes to chemotherapy-induced cell death is highly controversial. Autophagy was identified by enhanced expression of LC3B-II, an autophagosome marker, an increase in the formation of acridine orange-stained cells, indicative of increased vesicle formation and electron microscopic confirmation of autophagic structures. The vacuolar H+ ATPase inhibitor bafilomycin-A1 (BAF-A1) inhibited vesicle formation and enhanced the apoptotic potential of PBOX-6. These findings suggest a cytoprotective role of autophagy in these cells following prolonged exposure to PBOX-6. Furthermore, BAF-A1 and PBOX-6 interactions were determined to be synergistic and caspase-dependent. Potentiation of PBOX-6-induced apoptosis by BAF-A1 was associated with a decrease in the levels of the anti-apoptotic protein, Mcl-1. The data provide evidence that autophagy functions as a survival mechanism in colon cancer cells to PBOX-6-induced apoptosis and a rationale for the use of autophagy inhibitors to further enhance PBOX‑6‑induced apoptosis in colon cancer.
authors.affiliation: School of Biochemistry and Immunology, Trinity Biomedical Sciences Institute, Trinity College Dublin, Dublin 2, Ireland.
authors.forename: Lisa M
authors.initials: LM
authors.lastname: Greene
authors.forename: Derek P
authors.initials: DP
authors.lastname: Nolan
authors.forename: Daniel
authors.initials: D
authors.lastname: Regan-Komito
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Campiani
authors.forename: D Clive
authors.initials: DC
authors.lastname: Williams
authors.forename: Daniela M
authors.initials: DM
authors.lastname: Zisterer
mesh_terms: D000230:Adenocarcinoma / Q000188:drug therapy* / Q000235:genetics / Q000473:pathology; D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D001343:Autophagy / Q000235:genetics*; D020169:Caspases / Q000378:metabolism; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects; D003110:Colonic Neoplasms / Q000188:drug therapy* / Q000473:pathology; D004357:Drug Synergism; D006801:Humans; D008247:Lysosomes / Q000378:metabolism / Q000473:pathology; D018942:Macrolides / Q000008:administration & dosage*; D051379:Mice; D008869:Microtubule-Associated Proteins / Q000378:metabolism; D010077:Oxazepines / Q000008:administration & dosage*; D011758:Pyrroles / Q000008:administration & dosage*
chemical_list: C502070:MAP1LC3B protein, human; D018942:Macrolides; D008869:Microtubule-Associated Proteins; D010077:Oxazepines; D011758:Pyrroles; C040929:bafilomycin A1; D020169:Caspases; C418868:PBOX-6